The present invention relates to a washer based nut comprising a washer that is combined with a nut body for use is fastening wooden articles such as foundations of wooden houses to certain anchor bolts whose feet are embedded in and secured to a footstall.
In general, the washers combined with such wooden article-fastening nuts must have a sufficient diameter and sufficient thickness so as not to `cut` into those wooden foundations when said nuts are forcibly driven and tightened on the anchor bolts. According to the current standards, those nuts for instance of `M14` class must be used with round steel washers 4 mm thick and having a diameter of 45 mm or, alternatively, with square steel washers also 4 mm thick and having a size of 45 mm.times.45 mm. The wooden foundations, and more particularly their portions thus pressed with those washers and nuts, may tend to become slender and lower the fastening effect thereof in the course of time. Therefore, an annular leaf spring has been interposed between each of those large washers and the nut body, in order to compensate any significant reduction in thickness of those foundation portions.
FIG. 5 shows one example of the prior art washer based nuts of the described type. In this example, a nut body 1 is attached to a large washer 3 serving as the `base` for the nut body, with an annular leaf spring seat 2 intervening between them and these three parts forming an integral unit. Since each nut body is freely rotatable on and relative to the washer, such nut units reduce labor in construction works and are convenient to manage their parts.
However in the prior art washer based nut shown in FIG. 5, the nut body 1 must comprise a tall cylindrical boss 4 continuing therefrom towards the washer that has to be combined with the nut body. The rim defining a free open end of this boss has to be deformed uniformly and centrifugally within the washer 3 underlying the spring seat 2. The step of deforming the cylindrical `boss` end in this way is somewhat difficult and noticeably raises overall manufacture cost. A round recess 5 formed in the bottom of washer 3 and around the central bore thereof for rotatably receiving the cylindrical boss 4 does leave there a thin annular shoulder 6. Since this thinned shoulder is subject to a strong thrust imparted thereto when fastening the nut, it has been difficult for the central portion of the washer to realize its full strength inherent in the increased thickness.